This invention relates generally to chemically amplified positive photoresist (or xe2x80x9cresistxe2x80x9d) compositions for use in lithography and a process for its use in the manufacture of integrated circuits. The invention additionally pertains to blends of polymers useful as binders in resist compositions, to novel resist compositions containing the polymer blends, and to methods for using the resist compositions to generate a resist image on a substrate.
The currently available chemical amplification positive resist compositions usually contain as a binder consisting of a copolymer or a terpolymer having a base-soluble functionality and/or a dissolution-inhibiting functionality, and a photoactive acid generator. These resist compositions are used for transferring images to a substrate, such as in the manufacture of high circuit density microelectronic devices. In general, a coating layer of the resist composition is formed on a substrate, and the layer is then exposed to radiation through a photomask incorporating a pattern. Exposure to the radiation induces a chemical transformation of the composition thereby transferring the pattern of the photomask to the resist coating on the substrate. After exposure, the photoresist is developed to provide a relief image that permits selective processing of the substrate.
The resist can be positive acting or negative acting. In a positive resist, the area exposed to radiation becomes more soluble in a developer solution while the area not exposed remains essentially insoluble. The solubility differentials between the exposed and the unexposed areas is attained by a deprotecting reaction of the polymer. The disadvantages of the positive resist composition includes cleavage of a substantial mass of the resist as a result of the deprotection reaction, which in turn can cause significant shrinkage of the area of the resist coating layer exposed to activating radiation. An alternative to positive resist composition is a negative-acting resist where the resist polymerizes or crosslinks upon exposure to radiation.
Thus, the area exposed to radiation becomes less soluble in the developer solution than the unexposed portions.
The binder component of the resist is usually a co-polymer, with the poly(hydroxystyrene-co-t-butyl acrylate) polymer being one of the most widely used. The poly(hydroxystyrene-co-t-butyl acrylate) polymer has a high dissolution rate when exposed to radiation. However, the polymer exhibits poor quality in printing isolated lines, thereby making it unsuitable for the fabrication of logic devices. In addition, it is subject to shrinkage.
As an alternative, a binder consisting of a terpolymer, such as poly(hydroxystyrene-co-t-butyl acrylate-co-styrene), has been utilized. However, terpolymers are inherently more complex than co-polymers in structure and their microstructure is more difficult to predict and control. Furthermore, control of the physical properties of terpolymers, especially their dissolution rates, requires precise control of the composition that is determined by the polymerization procedure.
The constraints associated with the use of terpolymers could be overcome by the use of a blend of two or more different polymers that exhibit the desired properties. In addition, the blend would be more economical to manufacture and use, and the physical properties could be more easily controlled. However, different polymers are generally immisible with each other and have a strong tendency to phase-separate. Thus, it is difficult to obtain a homogeneous blend of two polymers that could function as a resist.
Accordingly, it would be desirable to have a resist composition containing as a binder homogeneous blend of two or more polymers that exhibits enhanced lithographic performance and/or resistance to etching environments. Further, it would be desirable to have a chemically amplified positive resist formulation that does not exhibit significant shrinkage during exposure and other processing steps, and that forms highly resolved isolated lines suitable for the fabrication of integrated circuits.
The present invention relates to a photoresist binder composition comprising a homogeneous blend of (i) a copolymer comprising a first monomer that is a substituted or unsubstituted hydroxystyrene and a second monomer containing an acid labile group, preferably pendant to the polymer backbone, and (ii) and a phenolic polymer, that is optionally partially or wholly protected, such as polyhydroxystyrene, poly(hydroxystyrene-co-styrene), poly(hydroxystyrene-co-styrene-co-t-butyl acrylate), novolac, and the like.
The invention additionally relates to a lithographic resist composition, comprising a photoresist binder composition as above, and a radiation-sensitive acid generator which generates an acid upon exposure to radiation.
In a further embodiment, the present invention relates to the use of the novel resist composition to make integrated circuits. One such process involves the steps of (a) coating a substrate with a film comprising the aforementioned lithographic resist composition; (b) exposing the film selectively to a predetermined pattern of radiation to form a latent image therein; and (c) developing the image using a suitable developer composition. Step (b) involves the use of x-ray, electron beam or ultraviolet radiation, preferably xe2x80x9cdeepxe2x80x9d ultraviolet radiation having a wavelength of less than about 300 nm, more preferably having a wavelength of 248 nm.